1. Field of the Invention
This invention relates to a fluid control solenoid valve used for controlling the quantity of fuel to be injected into an internal combustion engine, and more particularly to such a solenoid valve used for spilling fuel under high pressure at an arbitrary timing in each cycle of operation of a fuel injection pump through which fuel is injected into cylinders of engine, such as a diesel engine.
2. Prior Art
The concept of injection amount control system of the type arranged to let high pressure fuel directly spill by way of a solenoid valve is known in the art of fuel injection into an internal combustion engine, typically a diesel engine. For instance, Japanese Patent Provisional publication No. 51-34936 discloses such fuel injection system for a diesel engine. According to the above-mentioned system a solenoid valve is provided in a passage communicating between a high pressure chamber of a pump and low pressure side, and the solenoid valve is opened after either an arbitrary given period of time or the rotation of a cam angle from an instant of a reference angle signal generated at a given timing within an operation cycle of the pump so that high pressure fuel is spilled to control the amount of injection fuel. This known system is simple in construction when compared with conventional mechanical governor used for controlling fuel injection amount by positioning rack or sleeve, and is also suitable for electronic control.
The above-mentioned high pressure direct spill system has a problem in connection with how to maintain valve-closed state withstanding the pump chamber pressure of a diesel injection pump which is subjected to at least 200 to 400 kg/cm.sup.3, and how to readily manufacture a small-sized solenoid valve of high reliability which operates with response of 200 Hz at maximum depending on engine rpm. Furthermore, such a solenoid should have a structure so that valve is closed on energization, i.e. an acting direction opposite to normal fluid control valve, such that fuel injection is terminated when no electrical signal is applied due to breaking of wire or the like thereby stopping a motor vehicle in a safe manner. Although a solenoid valve with quick response was proposed in Patent Publication No. 59-211724, this solenoid valve does not have a structure of closing the valve on energization.
Although a solenoid valve of the type arranged to close on energization is known from Japanese Patent Provisional publication Nos. 59-211724 and 59-211757 as well as U.S. Pat. No. 4,480,619, the diameter of a needle arranged to push a ball valve head is necessarily smaller than the diameter of a valve seat associated with the ball valve, and thus such valve structure is difficult to treat fluid under high pressure because of low reliability.